Caustic bath



Oct. 27, 1931. M. W. WARD 1,829,693

CAUSTIC BATH Filed Sept. 29, 1930 Fig. Z

Inventor.

Montagnana Ward.

by Hisv Attorney.

Patented Oct. 27, 1931 narran STATES MONTAG-UE WESNEY WARD, OF ERIE, PENNSYLVANIA, ASSIGNOIL TO GENERAL EIEC- TRIC COMPANY, A CORPORATION F NEW YORK Application led September 29, 1930. Serial No. 485,052.

The present invention relates to the disintegration of siliceous materials and is particularly applicable to removal of vitreous materials, such as enamel, sand or the like,

from metal objects.

Heretofore serious diiliculties have been encountered When attempt has been made to employ fused caustic alkali for the removal of siliceous material from metal, as the fused alkali, which at the outset is highly chemically active, became so sluggish chemically as to be unt for further use When only a small part of the alkali had been consumed.

I have discovered that such a bath may be revivified, or continuously maintained in an active chemical state by adding Water, preferably in the form of low pressure steam, to the bath either intermittently or continu- 'ously during operation. My invention oomprises an apparatus and a process for removing vitreous coatings from metal objects as hereinafter more fully described.

The accompanying drawingsv illustrate an apparatus suitable for use in carrying out my invention, Fig. l being a vertical section and Fig. 2 a cross section taken on lines 2-2 of Fig. 1.

The apparatus illustrated comprises an external housing 3 of suitable refractory material provided with a metallic casing 4. Supported Within the housing 3 and spaced away therefrom at its sides is a tank 5 consisting o f steel, or other suitable alkali-resistant material.V An electric resistance heater 6 is supported on hangers 7 projecting from the housing 3 into heat-radiating relation to the tank 5. Suitable control devices (not shown) are employed to regulate the energy input for the heater and to maintain a desired temperature.

Within the tank 5 is placed a bath, (not shown) of suitable caustic alkali, as for example sodium or potassium hydroxide or a mixture of such hydroxides. The bath should be maintained at a suitable operating temperature Which may be generally said to fall Within the range of 450 to 1000'o C., the particular temperature chosen depending on Ythe conditions, such, for example, as the chemical character of the Work, its thickness,

size and other properties. In general, I prefer' for the stripping of siliceous enamel from sheet metal to employ a temperature of about 550 to 600o C.

Dry steam at a pressure slightly above atmospheric rpressure may be vintroduced to maintain the caustic bath in an active convdition iscontinued during the period of use of the bath. Preferably a moderate excess of steam is supplied during the Working period, the excess being carried away by evaporation at the surface of the bath as long as the Working temperature is maintained. In other Words, at a Working temperature Within the range yabovegiven a bath of fused caustic can only become associated With a fixed percentage of Water, Vany excess over this amount being evaporated. By thus continually supplying Water (preferably as steam) to the bath the initial activity of the fused caustic is readily maintained until the bath becomes exhausted of alkali. Ordinary vitreous enamel coatings are removed in the course of one to tWo minutes. When the enamels to be removed contain lead compounds, steam preferably is introduced intermittently, i. e., between periods of use of the bath to avoid stirringthe bath and bringing reduced lead into contact With the cleaned metal.

My invention is applicable to the removal of surface coating of various siliceous, or vitreous materials, including the removal of adherent vsand from metal castings and in general to any process involving the chemical disintegration of siliceous materials.

The by-products of the chemical reaction of the alkali With the siliceous material sink to the bottom and should be removed from time to time.

While I do not Wish to be limited by any chemical theory7 I believe that by the chemical reaction of the hydroxides of a fused alkali bath With siliceous materals hydrated compounds are formed decomposing the hydroXides of the alkali metal and forming X- ides. These oXides'are inactive chemically vvith respect to siliceous materials. The addition of Water to the bath by chemical combinatio'n'with the oxides reforms hydroxides m h'eleb'y restoring the chemical activity of theV What I claim as new and desire to secure by Letters Patent of the United States, is,-

l. In the process of disintegrating sili'- ceous material by chemical combination with fused causticalkali the step Which consists in revivifying the chemical activity of caustic alkali by adding Water thereto.

2. In the Vprocess of removing siliceous o material from metal objects by the chemical effect of caustic alkali at a Working temperay ture above about 450 C., the step Which conl sists in revivifying the alkali after it has become chemically sluggish with respect to said Y siliceous'material by supplying steam thereto While maintaining said alkali at said Work ing temperature.

Y 3. In the process of removing fusedenamel from metal objects by the chemical eect of 3U a bath of caustic alkali at a Working ten'iperan ture Within the range of about 550 to 600 C. the step Which consists in maintaining said bath chemically active by satura-ting the same With steam at its Working temperature.

Ll. The process of removing 'used enamel lfrom metal objects' Which comprises subjecting said objects to the chemical effect of a bath of caustic alkali at a Working temperature Within the range of about 550 to 600 C.

40 and maintaining said bath chemically active by continuously supplying the same With steam at its Working temperature. Y

In Witness whereof, I have hereunto set my hand this 26 day oSept.7 1930. MONTAGUE WESN'EY W'ARD. 

